To suppress signal reflection caused by an integrated circuit device on a reception or transmission side, a bus used for transmitting a signal between different integrated circuit devices (e.g., a microprocessor, a chipset, a memory, a memory controller, a graphic controller) may be terminated by a termination resistor. Signal reflection negatively influences signal integrity. In particular, in a system supporting a high-speed operation, signal reflection negatively influence signal integrity even more. Therefore, it is necessary to terminate a bus for transmitting a signal. Generally, a termination resistor should be provided to a bus which is adjacent to an integrated circuit device as close as possible in order to suppress the signal reflection (or in order to certainly terminate a bus).
In recent years, there is an increasing demand to shrink the dimensions of non-volatile memory devices such as a microprocessor or an application specific integrated circuit (ASIC). A ball grid array (BGA) has been developed as a semiconductor package to meet this demand. The BGA is an array in which external ports (balls-shaped lead) are disposed on the bottom side of a package so as to be amenable to a multi-pin arrangement. The BGA-type semiconductor integrated circuit package adopts a pin grid array (PGA) concept as well as a flip chip concept. As compared with a conventional quad flat package (QFP), the BGA-type semiconductor integrated circuit package is advantageous to reduce a space occupied by a semiconductor package, improve electrical and thermal conductivity, and save cost in a multi-pin arrangement (300 pins or more).
In a conventional BGA package, external ports disposed on the bottom side of a package are electrically connected to bus lines. When the bus lines are terminated, external ports closely disposed at a center of the package are relatively far away from corresponding termination resistors as compared with external ports adjacent to edges of the package. That is, remaining bus lines exist between the external bus lines disposed at the center of the package and their corresponding termination resistors. The remaining bus lines result in a signal reflection. Thus, in a case where the BGA-type semiconductor integrated circuit package is used, a termination structure to enhance a signal integrity may be necessary. To meet this demand, an on-die termination structure has been suggested in which a bus is terminated. As used here, the term “on-die termination” may be synonymous with “on-chip termination” or “active termination”.
An example of the on-die termination structure is disclosed in the U.S. Pat. No. 6,157,206 entitled “ON-CHIP TERMINATION”, in which an semiconductor integrated circuit device includes an on-chip input buffer, a termination circuit, and an impedance control circuit. The termination circuit is constructed in the integrated circuit device to terminate a bus line coupled to the input buffer. The impedance control circuit is coupled to an external reference resistor and controls the impedance of the termination circuit to have the same value as the external reference resistor.
The input buffer (or an output buffer) and the termination circuit may be disposed around a pad so as to reduce an effect caused by a noise at a long signal line.